The objectives of the research program proposed here are twofold: 1. An analysis at the electron microscopic (EM) level of synaptogenesis in the chick optic tectum during normal embryonic development using EM autoradiography (EMAR). The data will be used to test the predictions of two hypotheses of neural specificity: Do axons form connections with the first neurons they encounter during development, or do they show a more selective pattern of synapse formation? 2. Light microscopic (LM) and EM studies of the normal morphology of two visual centers, the ectomamillary nucleus and the ventral lateral geniculate nucleus, which show remarkably different responses to deafferentation during embryonic development. Subsequent experimental studies will analyze the changes taking place in both of these nuclei following optic-cup ablation in order to further investigate the importance of morphological factors in the maintenance of nerve cells by their afferent input during development.